# include<cs50.h>
# include<stdio.h>
# include<string.h>
# include<ctype.h>
char ciphertext;
char ascii;
char character;
char cliphertext;




int main(int argc, string argv[])
{
    if(argc == 2)
    {
        string k = argv[1];

        {
            for (int l = 0, m = strlen(k); l < m; l++)
            if (!isalpha(k[l]))
            {
                printf ("Please enter alpha.\n");
                return 1;
            }
            else
            {
                printf("Plaintext: ");
                string plaintext = get_string();


                for (int i = 0, n = strlen(plaintext); i < n; i++)

                {
                    if (isalpha(plaintext[i]))
                    {
                        if(isupper(plaintext[i]) && isupper(k[l]))
                        {
                            printf("%c", (((plaintext[i] - 65) + (k[l] - 65)) % 26) + 65);
                        }
                        else if(isupper(plaintext[i]) && islower(k[l]))
                        {
                            printf("%c", (((plaintext[i] - 65) + (k[l] - 97)) % 26) + 65);
                        }
                        else if(islower(plaintext[i]) && islower(k[l]))
                        {
                            printf("%c", (((plaintext[i] - 97) + (k[l] - 97)) % 26) + 97);
                        }
                        else if(islower(plaintext[i]) && isupper(k[l]))
                        {
                            printf("%c", (((plaintext[i] - 97) + (k[l] - 65)) % 26) + 97);
                        }
                    }
                    else
                    {
                        printf("%c", plaintext[i]);
                    }
                }
                printf("\n");
            }
        }
    }
    else
    {
        printf("Error\n");
        return 1;
    }
}